NeoPhotonics is buying a semiconductor optical components division of Japan’s Rohm Co. for $36.8 million, saying Tuesday that the purchase could give it better tools for telecommunications customers.

The unit, which is part of Rohm subsidiary Lapis Semiconductor Co., provides lasers and other devices for high-speed communications networks.

NeoPhotonics Corp., which makes components for communications networks, said the deal could also strengthen its existing customer base in Japan. The San Jose, Calif., company plans to fold the unit into its semiconductor subsidiary located near Tokyo.

It will pay $21.2 million in cash now and $15.6 million over three years for the Lapis Semiconductor optical unit, which includes patents, a plant and related real estate.

Both companies’ boards have approved the acquisition, which is expected to close by the end of June.

Shares of NeoPhotonics dropped 23 cents, or 4 percent, to $5.51 in morning trading.